Rectifier



Dec. 27, 1938. w. LEUKERT RECTIFIER Filed March 4, 1937 lam/3K PashaDec. 21 1938 I 2,141,921

UNETEB STATES PATENT QFFICE RECTIFIER Wilhelm Leukert, Berlin-Siemensstadt, Germany,

assignor to Siemens-Schuckertwerke Aktiengesellschaft,Berlin-Siemensstadt, Germany, a corporation oi. Germany ApplicationMarch 4, 1937, Serial No, 12%,919 In Germany March 2, 1936 6 Claims.(Cl. I'M-$64) My invention relates to rectifiers in which the, twocurrent limiting devices are, for instance, periodical connectionbetween the alternatingprovided, since at most two of the six phasescurrent supply circuit and the direct-current suppartake simultaneouslyin the process of rectiply circuit and the direct-current consuming dofication. The number of the required current vice is not established byelectric discharge devices limiting devices must be greater in casemeans are 5 with valve effect but by circuit breakers which are providedwhich introduce additional voltages into actuated in synchronismwiththealternating-curthe individual phases and which thereby cause rentsupply circuit. It has already been proposed an extension of the currentsupply period in each when using such rectifiers to insert between thephase as compared with the ordinary polyphase l0 direct-current supplycircuit and the alternatingcircuit. This effect may be produced forinstance 10 current supply circuit devices which serve to limit bydissolving the secondary winding of the transduring the rectificationthe current to be periodiformer into two star-connected systems of halfcally interrupted to such a value as to permit the number of phases,which star systems are the interruption of the current by circuitbreakshifted against one another one half of the ers. As a currentlimiting device, a saturated phase angle. The star points of such adissolved 15 reactor may be employed or a reactor which is system areconnected by means of a throttle, the equipped with a secondary windingseparately center point of which is provided with a tab. excited. Thiscenter tab of the throttle then constitutes When using suchrectifiersior the rectification the zero. point of the transformerwinding. With of polyphase alternating-current voltages, the such anarrangement, for instance, if two three- 20 number of the currentlimiting devices is chosen phase star windings are used, a six-phasesystem according to the invention considerably smaller is produced, theindividual phases of which, howthan the number of thealternating-current ever, act with respect to the duration of thecurphases which are successively rectified during the rent supply as thephases of an ordinary three transmission of energy. According to theinvenphase system. While, however, in ordinary trans- 25 tion the numberof the current limiting devices is former connections, at mostnamelyduring the equal to the number of the alternating-current Overlappperiod of the phaSeS-tWo phases phases which are at most at a givenmoment simultaneously carry current, in a transformer involved in theprocess of rectification. Between with a throttle as describedhereinabove, or with the alternating-current phases and the currentarrangements which have a similar effect, time 30 v limiting devices areinserted-circuit breaker con- P s exist, owing to tho oXtendod e tptacts which are connected to one another, to the ply period in eindividual phases, Within Wh c alternating-current source and to thecurrent more than tWo phases are able to C y mu limiting devices in sucha manner that the curyrent limiting devices are periodically connectedIn Figs- 1 and 2 of the accompanying ing 35 in succession to thedifferent alternating-current are Shown embodiments, of y invention indiaphases. Besides these circuit breaker contacts grammatio form- In atransformer 2, particular auxiliary circuit breakers may be con- WhoseSecondary Winding arranged i i nected in series with the currentlimiting devices, phase Star Connection, is Connected to an alter- 40which auxiliary circuit breakers eifect the internoting-current ppcircuit w n the 40 ruption of the current, whereas the other circuitdirect-Current Supply Circuit 3 and t Secondary breaker contactsdirectly connected tothe alterphases of the transformer 2 are nsertedtwo mating-current phases serve only as selector reactors 4, which serveto limit the current, and switches in order to connect the currentlimiting SWitohing goal 5 Consisting p u al ty of devices to thealternating-current phase which is circuit bieaker contacts The tw a trs 4- a're 45 about to be involved in the process of rectificadesignedso that y e already Saturated at tum, a comparatively small currentdensity and that The number of the current limiting devices to theydistort the current wave to such an extent be inserted between thecircuit breakers and the that the current flowing through them at 01direct-current supply circuit and the direct-cure the time of break isSo Small t t can 50 rent consuming devices depends greatly upon the beinterrupted with practically no sparking at connection employed for thealternating-curthe contacts. For any currents above the saturarentphases feeding the arrangement. In case tion value, these reactors donot constitute an a normal six-phase star connected transformerappreciable impedance for all practical purposes.

is employed for supplying energy to the rectifier, The-switching gear 5consists of eight individual 55 switches 8-l5 designed in the form ofcam switches, six switches 8-l 3 of which are connected to the secondaryphases of the transformer 2 and two switches l4 and [5 to both reactors4.

5 These switchesare controlled individually by a cam shaft driven by asynchronous motor 6 whose alternating-current winding is connected tothe three-phase current-supply circuit I through a regulatingtransformer 1 for the purpose of properly timing the operation of theswitches with the frequency of the supplied alternating current.

This arrangement operates as follows:

In the position of the switch gear shown, contacts 8 and I5 are closed,so that the phase of the transformer secondary winding which isconnected to contact 8 is connected by way of the left hand throttle 4with the direct current systern. After a given time period, the nextfollowing contact 9 is closed by the switch gear, and at the same time,contact 14, which is electrically connected with contact 9, is closed.Thereby a local closed circuit is formed in which a voltage is effectivewhich is equal to the difference between the voltages of the phaseswhich are connected to contacts 8 and 8. In this local circuit, the tworeactors-4 are connected in series. If we assume for the purpose of thepresent explanation that the current which flows in the direct currentcircuit is made completely smooth, i. e., that it is without anyripples, the sum of the currents which flow in each instance through thephases which are simultaneously connected in circuit by the contacts 8and 9 must have a constant value and must be equal to the value of thedirect current flowing at that time. The pre sumption for the correctmode of operation of this arrangement is that the time period at whichthe phase contact 9 is closed is selected so that the voltage differenceeffected in that circuit is polarized in such a direction that it tendsto produce in the contact 8 a direction of current which coincides withthe direction of the direct current.

So long as contact 8 is alone closed, the entire direct current flowsover this contact. However, at the instant when contact 8 is closed inaddition, a short circuit current develops in the local circuitincluding the reactor 4, which short circuit current flows first as theonly current through contact 8, which latter was formerly without current. This short circuit current, however, flows in the oppositedirection from the current which flows in contact 8, and thereforegradually neutralizes and eliminates this latter current. It should benoted, however, that this short circuit current is not generated by anymeans suddenly, but only gradually owing to the inductance contained inthe local short circuit so that the current which flows through contact8 is gradually diminished to zero, while the current flowing throughcontact 8 rises within the same time period to the full value of thedirect current.

As explained hereinbe'fore, the reactors 4 are designed so that when thevalue of a comparatively small current traversing the reactor isexceeded, a value at which the contacts may be safely opened practicallywithout producing sparks, these reactors suddenly attain full saturationbeyond which they do not form any appreciable impedance for the currenttraversing them. Immediately after contact 8 has been closed, thecurrent flowing through this contact is still be low the saturationcurrent value of the reactor which is in series with this contact, andthere 75 fore this reactor still has its full impedance. The

effect of this is that the current flowing through these contacts atfirst varies only very slowly, until the current flowing through contact8 exceeds the saturation point of the reactor and thereupon the latterloses its high impedance suddenly down to a very small and negligiblevalue. Thus from this point a very much faster variation of the currentflowing through the two contacts becomes possible. After a given timeperiod the current in contact 8 and thus in the right hand reactor coil4 has dropped far enough below the saturation point of this throttle sothat its full inductance comes suddenly into ef fect. From that momenton, they current variation proceeds again only very slowly and thus thecurrent flowing through contact 8 remains near its zero value for aconsiderable time period, and thus at a value at which sparkless openingof the contact is still possible.

Within this aforementioned time interval, during which the left handreactor 4 has its full inductive eifect, contact 8 must be opened sothat now only contact 8 remains in circuit. Subsequently, contact l8takes over the function of contact 9 previously described, wherebycontact I is connected by way of contact I with the left hand reactorcoil 4. In this manner, contacts 8 through l3 are successively closed,and contacts [4 and I5 are alternately connected with the contacts 8through l8. During the overlapping period of two phases, respectivelyduring the overlapping of the closing periods of two contacts, bothreactors are always connected in circuit and in series with one anotherin the local circuit produced during this overlapping period.

The particular form of switching gear 5 shown in Fig. 1 is shown only byway of example, and any other conventional form of controlled contactmechanism may be substituted. For instance the break contacts of thecircuit breakers inserted between the direct-current supply circuit andthe alternating-current transformer may also be designed in anothermanner; for instance so that the contact connection is establishedbetween a brush and a revolving contact as in the case of a. commutator.The main point is that the number of the current limiting devices 4connected in series with the direct-current supply circuit is smallerthan the number of the alternating-current phases feeding the rectifier.

Fig. 2 shows another embodiment of my invention. The parts correspondingto Fig. 1 are designated by the same numerals of reference. Thedifference between the two connections consists in the fact that in Fig.2 three, instead of two current limiting devices are provided, since thesecondary winding of the transformer 2 consists of two star-connectedthree-phase systems, the star points of which are connected together asmentioned at the beginning by means of a throttle I, provided with acenter tab' which leads to one pole of the direct current system so thateach of the six phases has a current supply period to the direct currentof 120". In this connection, three alternating-current phases partaketemporarily at the same time in the transmission of energy andaccordingly three devices for limiting the current to be interrupted bythe circuit breaker 5 are provided. The lower contacts of the circuitbreaker 5 are connected with one another and with the current limitingdevices in such a manner that only those contacts are connected inparallel relation to one another which cannot partake simultaneously inthe transmission of energy.

I claim: g

1. A converter for exchanging energy between a polyphase alternatingcurrent circuit and a direct current circuit, comprising a switchinggear having a plurality of contacts arranged to successively connect thephases of the alternating current circuit with successive overlappingphases and said impedances in series connection,

the time period for closing said local circuit being selected so thatthe voltage difference between the overlapping phases, prevailing insaid circuit, is polarized in the direction of the current in the directcurrent circuit,- and means for" selecting for said switch gear thedesired phase relation with the alternating current circuit.

2. A converter for exchanging energy between a polyphase alternatingcurrent circuit and a direct current circuit, comprising" a transformerincluding a primary winding connected to the alternating current supplycircuit and a plurality of secondary windings, each starconnected andshifted in phase with respect to the other secondary winding, aplurality of series-connected inductances inserted between the neutralpoints of said secondary windings and having their center point directlyconnected to said direct current circuit, a switching gear having aplurality of contacts arranged to successively connect the phases ofsaid secondary windings with successive overlapping of the phase contactperiods to the direct current circuit, means for driving said switchinggear in synchronism with the alternating current circuit, a plurality ofvariable impedances equal in number to the highest number ofsimultaneously overlapping phases, each impedance being series-connectedin the direct current circuit and designed to reduce the intensity ofthe commutating current which it carries, means for establishing aplurality of local closed circuits, each including in series two phasesconnected to the direct current circuit and two of said impedances, andmeans for selecting for the operation of all of said contacts thedesired phase relation with the alternating current circuit.

3. A converter for exchanging energy between a polyphase alternatingcurrent circuit and a direct current circuit, comprising a plurality ofbreak contacts severally connected to the phases of the alternatingcurrent circuit, said contacts being parallel-connected in groups, onlysuch contacts being connected in parallel relation to one another whosecorresponding phases do not carry current simultaneously, a number ofimpedances equal to the number of said groups of break contacts, anddesigned to reduce the intensity of the commutating current which itcarries, each impedance being series-connected in the direct currentcircuit, and a separate break contact for each of said impedances, meansfor connecting in succession the phases of the'alternating currentcircuit to the direct current circuit with successive overlapping of thephase contact periods and in synchronism with said alternating currentcircuit, and means for selecting for the operation of all of saidcontacts the desired phase relation with the alternating currentcircuit.

4. A converter for exchanging energy between a polyphase alternatingcurrent circuit and a direct current circuit, comprising a switchinggear having a plurality of contacts arranged to suecessively connect thephases of the alternating current circuit with successive overlapping ofthe phase contact periods to the direct current circuit so as to formtemporary short-circuits including the simultaneously closed contacts,means for operating said switching gear in synchronism with saidalternating current circuit, a number of variable impedances smallerthan the number of phases of said polyphase circuit but at least equalto the number of the simultaneously overlapping phases, said impedancesbeing connected to said switching gear so as to be included in saidtemporary short-circuits and being designed to reduce the intensity ofcurrent flowing through the contacts operated at the time of currentflow by saidswitching gear during an interval including the openingperiod of said contact, means for periodically connecting each of theimpedances to difierent phases, and means for selecting for said switchgear the desired phase relation with the supplied alternating current.

5. A converter for exchanging energy between a polyphase alternatingcurrent circuit and a direct current circuit, comprising a switchinggear having a plurality of contacts arranged to suecessively connect thephases of the alternating current circuit with successive overlapping ofthe phase contact periods to the direct current circuit so as to formtemporary short-circuits including the simultaneously closed contacts,means for operating said switching gear in synchronism with saidalternating current supply circuit, a plurality of reactors connected tosaid switching gear so as to be included in said temporaryshort-circuits and being designed to be saturated at low intensities ofcurrent, means for periodically connecting each of said reactors to adilferent phase, and means for selecting for said switch gear thedesired phase relation with the supplied alternating current.

6. A converter for exchanging energy between a polyphase alternatingcurrent circuit and a direct current circuit; comprising a switchinggear having a plurality of contacts arranged to successively connect thephases of the alternating current circuit with successive overlapping ofthe phase contact periods of at least two successive phases to thedirect current circuit so as to form temporary short-circuits includingthe simultaneously closed contacts, means for driving said switchinggear in synchronism with said alternating current circuit, a number ofvariable impedances equal to the number of simultaneously overlappingphases series-connected to the direct current circuit so as to beincluded in series connection with the simultaneously closed contacts insaid temporary short-circuit, said impedances being designed to reducethe intensity of the commutating current, means for establishing aplurality of local closed circuits, each including in series two phasesconnected to the direct current circuit and two of said impedances, andmeans for adjusting the desired phase relation of said switch gear withrespect to the alternating current circuit.

WILHELM LEUKERT.

